Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $232.58   10.837%   $257.7847   $257.78   $257.80   $257.80  
  Purchase #2 $121.49   11.623%   $135.6108   $135.61   $135.60   $135.60  
  Purchase #3 $206.54   9.205%   $225.552   $225.55   $225.55   $225.60  
  Purchase #4 $234.38   13.312%   $265.5807   $265.58   $265.60   $265.60  
  Purchase #5 $130.27   13.724%   $148.1483   $148.15   $148.15   $148.10  
  Purchase #6 $164.76   8.522%   $178.8008   $178.80   $178.80   $178.80  
  Purchase #7 $71.85   3.229%   $74.17   $74.17   $74.15   $74.20  
  7 purchase totals = $1,161.87       $1,285.6473   $1,285.64   $1,285.65   $1,285.70